Prosthetic dentistry involves the construction of crowns, caps, inlays, onlays, partial dentures, full dentures, implants, occlusion maintaining restorations, and fixed bridgework. The practice of prosthetic dentistry often requires recording accurate impressions (or molds) of a particular tooth, teeth, or implant for which an artificial prosthetic will then be fabricated at a dental laboratory. At the interface or limit line of the tooth (or root, or implant) surface to be worked on and the gingival margin (gum line), prior to impression taking, the gingival sulcus is often reflected or retracted with gingival retraction cord before flowing impression materials onto the tooth, teeth, or implant interface in order to register an accurate impression of the prepared tooth (or root, or implant) structure.
Following the taking of an impression in prosthetic dentistry, artificial prosthetic devices such as crowns, inlays, gold onlays, caps, dentures, implants, bridges, etc., are fabricated in a dental laboratory according to a master model poured from the impression. Following dental laboratory prosthetic fabrication, the prosthetic device is then delivered to the patient.
At delivery to the patient and during insertion of the prosthetic device onto or into the tooth structure, various cements are used to lute the interior portion of the artificial prosthetic (e.g. crown) to the prepared tooth which previously has been devoided of enamel and some dentin following "drilling" with, for example, water cooled dental burs attached to conventional high or low speed dental handpieces.
"Lute" and "luting" are art recognized terms which describe the attachment of dental materials or devices to one another and to prepared tooth structure by increasing the coefficient of friction between such materials or devices and tooth structure.
FIG. 1 is a side elevational cross-sectional view of a prior art tooth including crown 1 attached to prepared tooth structure 3. As shown, tooth structure 3 includes pulp 5 and extends upwardly from gingiva or gum line 7. Crown 1 is attached to prepared tooth structure 3 via cement or adhesive layer 9.
In clinical dental practice, an ongoing major concern is "washout" of cement 9 from gap 11. Gap 11 is that area which exists at the general level of the gingival cavosurface margin between prepared tooth structure 3 and the gingival limit of artificial crown 1. "Washout" is the dissolution of cement 9 via enzymatic, salivary, gingival crevicular fluid, mechanical or bacteriologic action. "Washout" leads to exposure of the soft part of the tooth structure, namely dentin 13 which may then erode and become subject to the colonization of caries (decay) producing bacteria at the Junction between the interior surface of the crown and the prepared tooth structure's gingival limit. When such recurrent marginal or submarginal caries occur, the tooth is placed at increased risk of penetration of bacteria into the dentin and subsequently the dental pulp resulting in endodontic (root canal) disease, bone infection, crown or bridge loosening, breakage of the crown or bridge prosthesis, and possible tooth or bridge loss. Thus, cement "washout" and its sequela of bacterial colonization in gap 11 is a significant concern which needs to be addressed.
In response to the problem of cement "washout", various glass ionomer (GI) cements 9, which permanently adhere prosthetics to prepared tooth structures, have been developed. Many GI cements are of the visible light cured (VLC) and self-curing type which provide cross-linkage in adhering materials to one another. Several of these known glass ionomer cements are formulated to combat washout and bacterial colonization by continually releasing fluoride so as to aid in the prevention of submarginal gingival caries following the placement of crowns or bridges in patients' mouths.
A problem associated with fluoride releasing GI cements is that they must be placed onto the prepared tooth structure when it is completely dry, and moisture must then be kept from the prosthetic prepared area for about 5-10 minutes in order to allow the GI cement to properly set. This condition is difficult to achieve due at least in part to the natural moisture inside the mouth created by the salivary glands, the natural ambient mouth moisture and due to the flow of gingival crevicular fluid within the periodontal sulcus or space.
An additional problem associated with the use of known glass ionomers or other similar prosthetic luting cements is that once these cements set, there is no way to remove the crown or bridge from the tooth other than to drill it off thereby destroying the prosthetic. The need to remove such a prosthetic from the tooth may arise, of course, when decay or periodontal disease develops after fixed prosthetic attachment.
A further reported problem in using these permanent cements (e.g. GI) is that there is a reported 7%-15% incidence of adverse endodontic (root canal) response associated with their use in teeth prepared for crowns and in teeth prepared as abutments for fixed partial dentures. Such adverse responses often require root canal therapy in order to retain the crown or bridge and to return the tooth to a healthy condition. When GI cements are used, for example, the crown or bridge cannot be removed for endodontic therapy except through partial or complete destruction of the crown (or cap) itself.
For example, when as shown in FIG. 1 a GI cement 9 is employed, it is often necessary to drill through the biting or occlusal surface of crown 1 in order to provide access to pulp chamber 5 of tooth 3 and its root canal(s) in order to perform root canal therapy. Thereafter, during endodontic therapy, the pulp chamber is subsequently enlarged inside of the remaining tooth structure thereby removing a significant portion of the previously prepared internal tooth structure which supports the crown or bridge which compromises the strength of the overall tooth root and crown during normal masticatory or parafunctional tooth contact. Root canal therapy using thin sterilized stainless steel files is then performed with eventual sealing of the root canal(s) using biocompatable endodontic sealing materials and cements.
Clearly, should root canal therapy be necessary in a tooth which has been restored with, for example, a crown which has been luted to the prepared tooth structure with a GI or other similar cross-linking cement, additional removal of internal supporting tooth structure which supports the crown or bridge decreases the biological support for the crown or bridge thereby placing the crown, bridge, etc. and tooth at increased risk for breakage or loss. It therefore would be desirable and easier if the practitioner did not have to drill through crown 1 in order to access pulp 5 of tooth 3 in order to perform endodontic therapy.
In order to overcome the above described problems associated with the use of GI cements, the use of zinc oxide based luring cements 9 has sometimes been advocated. Accordingly, when zinc oxide based luting cements 9 are used as in prior art FIG. 1, practitioners are able to remove crown 1 from tooth structure 3 if endodontic therapy is required, for example. In other words, the shear function of such cements is less than that of crown 1 and dentin 13 of structure 3 but is sufficient to adequately bond crown 1 to tooth structure 3 during masticatory or parafunctional demands so that crown 1 can be selectively sheared (i.e. removed) from structure 3 without destroying either. In such cases, crown 1 (or a fixed partial denture, etc.) can easily be removed intact due to the use of such a cement 9 and endodontic therapy can easily thereafter be performed. Following completion of root canal therapy after the intact removal of crown 1, if insufficient tooth structure remains, a restorative macrofilled resin core, or in the case of a tooth used as a bridge abutment, a laboratory fabricated cast post core, can be retrofitted to the interior portion of the crown or abutment. The post core can be cemented into the endodontically treated tooth, for example, and the original crown or bridge can be inserted easily back into the patient's mouth. Endodontic therapy following removal of the entire crown when temporary cement is used, therefore, will ensure better support for the endodontially treated tooth, root and crown, rather than weaken same as occurs when, for example, GI is used to lute prosthetics to teeth.
Unfortunately, a problem associated with the use of only zinc oxide based cements or other similar non-cross-linking cements for such applications is that "washout" again becomes a concern because such cements typically are more soluble to the influx of gingival and other oral fluids as previously described and do not release fluoride as do the aforesaid GI cements in an attempt to reduce the likelihood of washout and recurrent marginal or submarginal caries.
It is apparent from the above that there exists a need in clinical prosthetic and other dental practice (e.g. restorative dentistry) for a method and a system by which recurrent perimarginal gingival caries can be abated or prevented and which also allows for the nondestructive removal of crowns, bridges, caps, fixed partial dentures, gold onlays, fillings, etc. should, for example, adverse endodontic responses arise. In other words, there is a need for a system which would eliminate the aforesaid problems and allow practitioners to both (i) place a fluoride releasing system on the prepared tooth structure so as to prevent recurrent marginal gingival caries, and (ii) have the option to remove, for example, an artificial prosthetic device (e.g. crown) intact, should the inserted prosthetic be unaesthetic to the patient, should the crown or bridge fail to function properly in a patient's mouth after insertion, should peridontal disease develop around the tooth or around the teeth to which a bridge is attached or should an adverse endodontic response occur.
It is the purpose of this invention to fulfill the above-described needs in the art, as well as other needs which will become apparent to the skilled artisan from the following detailed description of this invention.